The objective of the research is to identify the neurotransmitter(s) utilized by cochlear and/or lateral-line hair cells to transduce information to the primary afferent nerves. Transmitter candidates will be evaluated using standard criteria with emphasis on: (1) neurophysiological evidence that the candidate mimics natural stimulation both at the action potential and membrane level, (2) pharmacological evidence that the candidate is antagonized by the same agents which antagonize natural stimulation, and (3) biochemical evidence that the candidate is released from hair cells during natural stimulation. The immediate health-relatedness of the project would be to patients suffering hearing loss due to deficiency of the transmitter substance.